{"arg":"factor", "description":"an integer corresponding to the darkening factor:<ul><li>if the factor is greater than 100, this function returns a darker color (e.g., setting factor to 200 returns a color that is half the brightness);</li><li>if the factor is less than 100, the return color is lighter, but using the lighter() function for this purpose is recommended;</li><li>if the factor is 0 or negative, the return value is unspecified.</li></ul>"}